I have a Trane X80 furnace with a Nest gen 3 thermostat. This combo has worked flawlessly for a summer and a winter. I just switched back to "cool" and the fan and compressor come on, but the fan stops after a few minutes (while the compressor continues to run). I contacted Nest and after a lengthy list of diagnostics, they determined that the Nest baseplate was bad and sent me a new one. I replaced it and the problem did not change. I pinged Nest again and they said that it must, then, be an HVAC problem. If I jump the fan wire (G) and power wire (R) wire, the fan runs for a couple minutes then shuts down. I'm guessing I have a fan going bad but just wanted to confirm before I replace it.

When you say "the fan", are you talking about the blower in the furnace or the fan in the condensing unit? When you say "a few seconds", how long exactly are you talking about? Does the fan get up to speed, or shut off just as it gets up to speed?
– Tester101Mar 27 '17 at 21:56

Sorry, yes...the blower motor in the furnace housing. Yes, the fan gets up to full speed, blows for about two minutes and then shuts off.
– GeekInTheBoxMar 28 '17 at 18:42